The present invention relates to a device for measuring the hydrostatic pressure in the amniotic sac during various stages of pregnancy for assisting in obstetric diagnosis. More particularly, the invention relates to a tocodynamometer having a strain gauge or other similar transducer therein wherein intra-amniotic pressure may be readily measured by merely strapping the apparatus to the patient.
Hydrostatic pressure measurements in the amniotic sac during various stages of pregnancy have been measured in the past by the use of catheters, balloons and pressure transducers which have been introduced directly into the uterus for such purposes. More recently, external pressure measuring devices have been used to perform the same functions under controlled conditions. One such external pressure measurement device is described in the "Journal of Obstetrics and Gynecology", volume 64, pages 59-66 (1957). This device is referred to as a "guard-ring tocodynamometer", which utilizes a pressure transducer centered in an outer guard ring, and a housing for supporting the outer guard ring, the housing having a slot for containing an elastic belt which may be attached about a patient. The foregoing paper describes the principles of operation and use of the guard-ring tocodynamometer, and illustrates the difficulty of obtaining proper use for such a device. The belt which attaches the device to the patient must be sufficiently tightened so as to develop an inward force sufficient to flatten the abdominal surface into virtually total contact with the outer guard ring so that intra-uterine pressure variations are transmitted to the pressure transducer, but not so tightly as to create inward forces which themselves affect the intra-uterine pressure. There is a relatively narrow range of external forces which are appropriate for proper attachment and measurement, and care must be taken to attach the device to the body so as to provide inward forces within this range.
If the procedure for attaching an external pressure measuring device to a patient is too complex there will arise a high degree of risk that the pressure readings are unreliable. Further, if the attachment procedure is too complex it will tend to discourage use of such devices in cases wherein the information provided by the device could otherwise be very helpful in medical diagnosis.
There is therefore a need for a tocodynamometer which may be easily attachable to a patient, and which gives reliable pressure readings without a complex attachment procedure. Further, there is a need for a tocodynamometer which may be readily used and reused within a medical practice, and which is capable of adhering to the principles of sanitation and cleanliness which are demanded of medical instruments.